1. Field of the Invention
The present invention relates to a communication system for performing redundant communication, a control station of this system and a communication method used in the system.
2. Description of the Related Art
A milliwave wireless technique using the 60-GHz band, in which a broad bandwidth can be utilized and high-speed wireless transmission is possible, has become the focus of attention as a technique for transmitting video and audio data. However, a problem with the milliwave is that owing to the strong linearity feature thereof, communication is easily interrupted when an obstacle such as a person crosses the path of communication.
In order to deal with this problem, a technique has been proposed by which data transmitted by a node that is the source of data generation is transmitted to a destination node redundantly using multiple communication paths with the intermediary of a relay node (for example, see the specifications of Japanese Patent Laid-Open Nos. 2008-131517 and 2009-049932). By virtue of this technique, if even one communication path is interrupted, data received from another communication path is used, thereby making it possible to improve communication reliability.
The wireless transmission of a large volume of data such as 4K2K or 3D video data in real-time has been considered as a high-end manner of use that is a further extension of the above-mentioned technique, and a broad communication band is necessary in order to perform redundant transmission and achieve an improvement in reliability. As a consequence, there is an increase in the amount of information and implementation by a single PAN (Personal Area Network) is difficult. Accordingly, redundant transmission utilizing multiple PANs having different frequency bands is required.
In a case where a large volume of data is transmitted redundantly in real-time using multiple PANs, the amount of data transmitted by a single node increases and a term of validity is imposed upon the data. Consequently, there is a tendency for the nodes that communicate using a single PAN to decrease in number. That is, since the number of times relayed transmission is performed by each node when redundant transmission is carried out in each PAN decreases, the reliability obtained declines and resistance of the communication path to interruption weakens. In order to improve the quality of redundant transmission in each PAN, therefore, it is essential to deploy nodes that make it possible to positively assure high-quality communication paths.
In a case where the conventional redundant transmission system is extended to a plurality of PANs, it is necessary to perform grouping of nodes in such a manner that each node can form more than the desired number of high-quality communication paths. If the combination of nodes allocated to each PAN is poor, nodes having few communication paths to other nodes will exist and there is a possibility for the resistance of communication paths to interruption to be weakened.